1. Technical Field
This invention relates generally to a pickup head adapted for use as a robot arm end effector, and more particularly to such a pickup head having a heated vacuum tip, and a method of using such a pickup head.
2. Background Art
The attachment of small electronic components, such as C4 (Controlled Collapse Chip Connection) devices, other flip chips and similar devices, to printed circuit boards (PCBs) or other substrate members currently requires several distinct assembly steps. First, soldering flux is applied to the electrical contacts of the chip and/or the substrate member. Next, the chip is acquired from a feed station and placed onto the substrate with high-accuracy positioning equipment. The adhesive properties of the flux hold the chip in place until it can be permanently soldered in place. Soldering is the final step of the attachment process. Depending on the production volumes and/or the capital investment, soldering is performed either via mass reflow or local reflow equipment.
A The term mass reflow means that all of the electronic components on a given printed circuit board are soldered simultaneously. Typically, solder required to make the permanent physical and electrical connection reaches reflow (melting) temperature via a conveyorized heating method. The primary advantage of this method is throughput, since a reflow oven doesn't care how many solder joints are soldered at one time. However, mass reflow processes require considerable capital investment in an oven and conveyorized handling equipment suitable for transporting components through the oven, and floor space. The flux used for flip chip attachment typically has very weak adhesive strength. Therefore, extreme care is required during transfer of chips between placement and reflow stations.
Local reflow methods have heretofore been slow, and as a result, costly. Convection heating, e.g. via hot gas flow and/or infrared elements, are used to bring the chip and the surrounding substrate area to solder reflow temperatures. Typically, this requires on the order of one to three minutes per chip. Depending on the chip size, the board location, and the proximity of the chip to other components, each chip is likely to require a unique heating profile, i.e., controlled heating element parameters such as gas flow rate, gas temperature, dwell time, and other process variables. Typically, the development of specific heating profiles requires many iterations before the process equipment is tuned to obtain the desired results, during the course of which many costly test samples are destroyed before the parameters are optimized.
The present invention is directed to overcoming the problems set forth above. It is desirable to have a means, including both and an apparatus and a method of using the apparatus whereby small electrical components can be attached to a substrate without subjecting previously attached components to a another heat cycle. It is also desirable to have an apparatus that can attach individual chips to a substrate without sacrificing the advantageous cycle time provided by mass reflow equipment. Furthermore, it is desirable to have a device that can pick up an electronic component from a supply source, transport the component to a work station at which a substrate is disposed, position the component with respect to a specific predetermined site on the substrate, and place the component on the predetermined site. Advantageously, during pickup, transport, positioning and placing, the component is simultaneously heated so that when the component is placed on the substrate, solder previously coated onto contacts on the component is heated to its reflow temperature. Alternatively, the component contacts are heated to a temperature sufficient reflow solder deposited on the substrate contacts. Thus, the total cycle time for placing an electronic component on a substrate is measured in terms of a few seconds rather than the previously required minutes.